J. Orq. Chem., Vol. 37, No. 15, 1972 2521
NOTES hydrogen directly to the enol exists but would require more energy. Experimental Sectiona Action of Sodium Methoxide on 3a,7a-Dihydro-3,3a,5,6tetraphenylinden-I-one (la).-The indenone l a (1 g ) was refluxed with sodium methoxide (0.01 g) in 95% ethanol (60 ml) for 30 min. The resulting brownish yellow solution upon cooling gave 3 (0.48 g) which after successive crystallizations from ethyl acetate and benzene melted a t 240-242’. This sample was identical with a sample prepared by the acid isomerization of l a 9 ir (Nujol) 1670 (C=O), 1650 cm-l (C=C); nmr (DCC18) 16 H z , H-4), 6.7-7.4 6 3.29 (d, J = 16 Hz, H-4), 3.62 (d, J ppm (m, 20 aromatic H and H-2). The filtrate upon treatment with water and a trace of acid gave 2, which after recrystallization two times from ethanol melted a t 176”, yield 0.16 g. This sample was identical with that obtained by pyrolysis:4 ir (Nujol) 1720 cm-’ (C=O); nmr (DCCla) 6 3.51 (s, CH1), 7.0-7.3 (m, 20 aromatic hydrogens), 7.4 (s, H-7), and 7.83 ppm (s, H-4). Heating a solution of the indenone l a (0.62 g) in 95% ethanol (35 ml) with sodium methoxide (0.01 g) for 8.5 hr gave 0.43 g of
vestigated the effect of internal base (in the form of neighboring carboxylate) on the oxidation of alcohols and aldehydes and have reported elsewhere the existence of such catalysis in the case of cis-2-hydroxycyclohexanecarboxylic acidU3 However, no such effect can be observed in the case of the anions of the ortho carboxy derivatives of benzaldehyde and benzhydrol, 1 and 2, as will be seen from the subsequent discussion.
1
2
3
4
The present brief report is prompted by the appearance of a paper which reports the presence of such intraAction of Hydrochloric Acid on 3a,7a-Dihydro-3,3a,5,6-tetra- molecular catalysis in the oxidation of 1 by b r ~ m i n e . ~ phenylinden-1-one (la).-The indenone la was heated in ethanol Comparison of the oxidation of the anions of 1 and 2 (50 ml) with concentrated hydrochloric acid (1 ml) for 17 hr. was made with the corresponding compounds lacking a Addition of water gave a solid (0.40 g) which, based upon the ir carboxyl group and with those containing such a group spectrum, consisted mainly of 2 with a small amount of 3 . in the para position. The results are summarized in 3a,7a-Dihydro-3,3a,5,6-tetraphenyliiden-l-one(la).-The nmr spectra in chloroform-d and benzene-& were identical with Table I. respect to integration. Chemical shifts for the vinyl hydrogen The effect of a carboxylate group on the oxidation of differed: nmr (DCC13) 6 3.54 (d, J = 5.5 Hz, H-7a), 5.98 (d, benzaldehyde in the neutral and mildly basic regions is J = 5.5 He, H-7), 6.18 (s, H-4), 6.8-7.5 (m, 20 aromatic H and small, whether the group is in the ortho or para posiH-2); nmr (CGDS)6 3.54 (d, J = 5.5 Hz, H-7a), 6.13 (d, J = 5.5 Hz, H-7), 6.40 (s, H-4), 6.8-7.5 ppm (m, 20 aromatic hytion. As the medium is made more acidic than pH 5 drogens and H-2); ir (Nujol) 1690 cm-I (C=O). the oxidation of all three compounds accelerates and becomes autocatalytic. The one striking effect of the Registry No.-la, 16643-52-0; 2, 16643-46-2; 3, ortho carboxyl group in phthalaldehydic acid is that at 16643-45-1. still higher acidities the oxidation rate for this com(3) Melting pointc, are not corrected. Infrared spectra were determined pound decreases again and the autocatalysis vanishes. on a Perkin-Elmer Infracord and Model 421 and nmr spectra were obtained A clean second-order reaction is observed at pH 1.55 with a Varian A-60 spectrometer. a t a rate that is considerably less than that observed (4) On occasion the ketone from the pyrolysis mas obtained in a crystalline form which melted at 153.5-155’. This sample upon standing in under neutral conditions. This is presumably due to 1 ethanol slowly changed into the 176’ melting form. The ir spectra mere existing under these conditions almost completely in the identical. This behavior explains the range of melting points reported by ring-closed phthalide form, 3,j a form whose oxidation Japps for this compound. (5) F. R. J a p p and C. I. Burton, J . Chem. Soc., 61,420(1887). behavior should resemble that of an alcohol rather than an aldehyde. I n the case of benzhydrol an ortho carboxy group has a pronounced inhibiting effect on the oxidation both in Neighboring Carboxylate Groups and the neutral and in basic solution. This effect cannot be due Oxidation of Benzhydrol and Benzaldehyde to the formation of the ring-closed phthalide compound, 4,6sincethis form predominates only below pH 5 , by Permanganate’ where, indeed, it precipitates from the reaction mixture and makes a study of its reaction with permanganate imJ. ANTHONY M A C P H E E AND ROSS STEWART* possible. The inhibiting effect of adjacent carboxylate Department of Chemistry, University of British Columbia, can be attributed to electrostatic repulsion between this Vancouver 8, Canada group and permanganate ion. Evidently, a specific conformational relationship between alcoholic hydroxyl and Received November 18, 1971 neighboring carboxylate is required before intramolecular catalysis of the permanganate-alcohol reaction can The permanganate- oxidation of both benzhydrol and be ~ b s e r v e d . ~ benzaldehyde is much faster in alkaline solution than at neutral pH. The activation of alcohols toward external Experimental Section base is due to formation of alkoxide ion.2 We have in2.
(1) The financial support of the National Research Council of Canada is gratefully acknowledged. (2) (a) R. Stewart, J . Amer. Chem. Soc., 79, 3057 (1957); (b) R. Stewart and R . Van der Linden, Dzscuss. Faraday Soc., 29, 211 (1960); ( 0 ) R. Stewart, “Oxidation Mechanisms, Applications t o Organic Chemistry,” W. A. Benjamin, New York, N. Y., 1964, pp 63-70; (d) R. Stewart in “Oxidation i n Organic Chemistry,” P a r t A, K. B. Wiberg, Ed., iicademic Press, New York, N . Y., 1965.
The rate measurements mere made by both iodometric and spectrophotometric means, essentially as previously described.2a,3 (3) R. Stewart and J . A. MacPhee, J. Amer. Chem. Soc., 93, 4271 (1971). (4) B. G. Cox, J . Chem. Soc. B , 1971, 1704. (5) (a) P . R . Jones, Chem. Rev., 63, 461 (1963); (b) D. D. Wheeler, D. C. Young, and D. S. Erley, J . O r g . Chem., 22, 547 (1957). (6) G. E. Resinger and J . A . Thompson, R e d . Trau. Chtm. Pays-Bas, 82, 801 (1953).
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J . Org. Chem., Vol. 37, No. 15, 1970
KOTES
TABLE 1 RATECONSTANTS A N D ACTIVATION PARAMETERS FOR THE PERMANGANATE OXIDATION OF VARIOUS COMPOUNDS IN WATER -----k,
Registry no.
Compd
pH 8.1
1. mol-1 sec-1, a t 259----7 pH 10.3 pH 12.7
AH*, koa1 mol-'
AS*,eu
Benzaldehydea 0.37 0.42 10.3b -26.25 119-67-5 Phthalaldehydic acid (1) 0.18 0.17 10.4c -27.1' 619-66-9 Terephthalaldehydic acid 0.28 0.39 11.2" -23.4' 91-01-0 Benzhydrold 0.070 0.10 3.7 e e 34737-60-5 Benzhydrol-2-carboxylic acid (2) 0.006 0.004 0.19 8.W -36.41 579-52-2 Benzhydrol-4-carboxylic acid 0.057 0.060 6.0 8.9f -32.41 a K. B. Wiberg and R. Stewart, J . Amer. Chem. Soc., 77, 1786 (1955). b At pH 6.5. e AH and A 8 * c At pH 8.1. d Reference 2a. for this compound are 5.7 and -38.4, respectively, at pH 12.3, a pH at which the oxidation proceeds almost entirely by way of the alkoxide ion. y At pH 5.45, for which k at 25' is 0.0237 and 0.139 1. mol-' sec-1 for the 2- and Psubstituted compounds, respectively.
*
The oxidations of 1 and terephthalaldehydic acid in water were allowed to proceed to completion nnd the organic products were isolated. The only products were phthalic and terephthalic acids, each being formed in near quantitative yield. I n the case of benzhydrol-2-carboxylic acid the reaction was quenched, at the aoint where the kinetic exaeriments showed the reaction to be 60% complete, by the addikon of sodium bisulfite and acid. The organic product was taken up in ether and this solution was
extracted with aqueous bicarbonate. The two fractions yielded 3-phenylphthalide and 2-benzoylbenzoic arid in qiiantitative amount corresponding to 60% reaction. The physical properties of the phthalide,B 2-benzoylbenzoic acid, and 4-benzoylbenzoic acid (formed in 98% yield by oxidation of 4-benzhydrolcarboxylic acid) were identical with those of authentic samples.
Registry No. -Permanganate, 14333-13-2.
